These studies are designed to describe the chemical characteristics of the Sex Steroid-Binding Protein (SBP) of human and Rhesus monkey plasma, and to explore its physiological role. The Rhesus monkey will serve as animal model since monkey and human SBPs are similar in their chemical properties and steroid-binding specificities. The first goal is to characterize the proteins and describe the chemical environment of the steroid-binding site to further understand the phenomeon of steroid-binding specificity. The experiments will involve chemical modification with "group specific" reagents and affinity labels to identify amino acid residues in the steroid-binding site. This will be achieved by isolating peptides comprising portions of the steroid-binding site followed by amino acid sequence analysis. Human SP will be crystallized in the hope of attaining "good" crystals for x-ray diffraction analysis. The second goal is to define the physiological role of SBP in the Rhesus monkey. Homogeneous SBP will be administered i.v. to monkeys and the effect on the metabolic clearance rate of testoterone (T) and estradiol-17 beta (E2) will be assessed. An SBP deficiency will be induced in the Rhesus by administering purified monospecific human-SBP antibodies or inducing passive immunization by long-term treatment with homogeneous human SBP. The clearance rate of T and E2 will then be assessed. The purpose of these experiments is to demonstrate an inverse relationship between SBP clearance rate of T and E2. The localization of SBP biosynthesis will be determined. Also the effect of SBP on gestation and parturition will be studied in the Rhesus. The results of these experiments should bring us closer to understanding the nature of this protein and its role in the mechanism of action of the sex-steroid hormones.